1. Field of the Invention
The present invention relates to a bandwidth control apparatus, a bandwidth control method, and a bandwidth control system for data transfer, and, more particularly to a bandwidth control apparatus, a bandwidth control method, a bandwidth control system applicable to subscriber data transfer systems of an x Digital Subscriber Line (x DSL) such as an Asymmetric Digital Subscriber Line (ADSL), a Symmetric digital Subscriber Line (SDSL), or a Very high-bit-rate Digital Subscriber Line (VDSL) and Fiber To The x (FTTx) such as Fiber To The Building (FTTB), Fiber To The Curb (FTTC), Fiber To The Cabinet (FTTC), or Fiber To The Home (FTTH). The x Digital Subscriber Line (x DSL) uses a metallic cable for a transmission medium to make it possible to perform high-bit-rate data transmission at several Megabits/second. The Fiber To The x (FTTx) uses an optical fiber cable for a transmission medium to make it possible to perform high-bit-rate data transmission at several tens Megabits to hundred Megabits/second.
2. Description of the Related Art
An overview of a general transmission system will be provided with reference to FIG. 1. FIG. 1 is a diagram showing an example of a network configuration of an Internet service provider including an access multiplexer.
Personal computers (PCs) 111 are placed in, for example, user homes. The PCs 111 connect to subscriber lines 109 serving as access lines through Customer Premises Equipment (CPE) 110. An Access Multiplexer (AM) 106 in a switching system terminates the subscriber lines and concentrates signals of the subscriber lines into a high-bit-rate transmission signal 105.
The AM 106 has a Line Termination Unit (LTU) 108 and an Integrated Gateway Unit (IGU) 107. The LTU 108 terminates the subscriber lines 109 which are the access lines from the user premises. The IGU 107 multiplexes a signal and performs protocol conversion for the signal as required.
The AM 106 transmits the multiplexed high-bit-rate transmission signal 105 to a switch or a router 104. Upstream signals from the PCs 111 in the user premises are transmitted to the Internet 103 through the CPE 110, the AM 106, and the switch or the router 104. Downstream signals from the Internet 103 to the PCs 111 are transmitted on a reversed route to the route from the PCs 111 to the Internet 103, that is, a route through the switch or the router 104, the AM 106, and the CPE 110.
A change of a usage pattern of the Internet and a change of a traffic pattern which is caused by the change of the usage pattern will be explained with reference to FIGS. 2 and 3. In FIGS. 2 and 3, a router or a switch is not shown because the router or the switch is unnecessary for explanation.
FIG. 2 is a diagram schematically showing a constitution of an Internet system including a server 201, a network 202, an access multiplexer 203, a multiplexed signal 204, access lines 205, and user terminals 206 in user premises, that is, the Internet for explaining a conventional typical usage pattern of the Internet.
The conventional typical usage pattern of the Internet is a client/server type in which the user terminals 206 in the user premises connect to the server 201 on the Internet 202. For example, users use the Internet in order to connect to the server 201 from the user terminals 206 and obtain information on the server 201. In such a usage pattern of the client/server type, upstream and downstream traffics are asynchronous. Specifically, the downstream traffics are extremely large compared with the upstream traffics. In other words, the downstream traffics are dominant in total traffics.
Therefore, in the conventional research and technology development for bandwidth control, researchers focused attention on bandwidth control for the downstream traffics that were dominant on the access lines 205 and had very little interest in bandwidth control for the upstream traffics.
In addition to the conventional usage pattern of the Internet shown in FIG. 2, in recent years, a new usage pattern of the Internet is increasing. FIG. 3 is a diagram schematically showing a constitution of the Internet for explaining the new usage pattern of the Internet that is frequently used in recent years.
The usage pattern of the Internet frequently used in recent years is Peer to Peer (P2P). Video conference, file exchange, and the like are typical applications of the P2P. In the case of the P2P, user terminals 301, 305, and 307 in FIG. 3 communicate with one another on equal ground over a network 303 via access multiplexers (AMs) 302, 304, and 306. In the usage pattern of the Internet of the P2P type, upstream traffics and downstream traffics are roughly equal. Therefore, bandwidth control for the upstream traffics becomes important for fairness of traffic allocation among users or for providing guaranteed bandwidth to each user.
Bandwidth control among access lines will be explained with reference to FIG. 3.
Many access lines represented by the xDSL provide services to users on a best effort basis. In the best effort services, a transmission rate of each of the user terminals 301, 305, and 307, that is, an effective rate, fluctuates depending on distances among the user terminals 301, 305, and 307, states of the access lines serving as transmission paths, and differences of conditions such as performance of the user terminals 301, 305, and 307.
For delivering the downstream traffics to each user terminal, the AMs 302, 304, and 306 usually transmit a multiplexed signal from the network 303 using broadcast to all of the access lines accommodated in each of the AMs 302, 304, and 306. Because of the broadcast, all of downstream bandwidth resources in the AMs 302, 304, and 306 are always shared by all of access lines accommodated in each of the AMs 302, 304, and 306. Therefore, the AMs 302, 304, and 306 can not perform bandwidth control on downstream for the access lines 308, 309, and 310 individually and optimize bandwidth allocation among the access lines any longer.
On the other hand, on the upstream traffics, signals are individually transmitted from the respective user terminals 301, 305, and 307 to the AMs 302, 304, and 306 using unicast. The AMs 302, 304, and 306 multiplex upstream signals from the user terminals 301, 305, and 307 and send out to the network 303. Therefore, concerning the upstream traffics, the AMs 302, 304, and 306 are able to perform bandwidth control for each of the access lines 308, 309, and 310 to adjust bandwidth allocation among the access lines. For example, if a user terminal uses out an upstream bandwidth and floods some of upstream traffic to bandwidth of the other user terminals, the AMs 302, 304, and 306 are capable of limiting bandwidths to equal to the respective access lines to provide fair service to each of the users.
However, a static bandwidth allocation of upstream traffics to the respective access lines, including the above-mentioned case which allocates the bandwidth evenly to the respective access lines for providing equal service to the users, may cause the waste of network resources. For example, the network resources are wasted when one end of downstream effective rate of the access line for any of user terminals 301, 305, and 307 which is transmitting data is lower than the other end of upstream bandwidths statically allocated to the access line of the user terminal which is receiving data from the other end.
When flow control is performed in this case, transmitting user terminal sends out data only at rate equal to or lower than the effective rate at the receiving user terminal and the statically allocated upstream bandwidth of transmitting side have a surplus. As a result, the surplus of the upstream bandwidths resources allocated statically to the line of the transmitting user terminal goes to waste. On the other hand, when flow control is not performed, regardless of transmitted data arrival at the receiving user terminals 301, 305, and 307, the transmitting user terminals send out data to the remote end at own rate. When the transmitting user terminal sends out data at a rate higher than the effective rates at receiving user terminals 301, 305, and 307, data sent out from transmitting user terminal is discarded at AMs 302, 304 and 306 before reaching the corresponding receiving end of user terminals 301, 305, and 307. As a result, the AMs 302, 304, and 306 waste bandwidth resources of the upstream for unnecessary transmission of data that do not reach the receiving user terminals 301, 305, and 307.
For another example, if bandwidth resources are allocated statically to access lines when communications among the user terminals 301, 305, and 307 is closed, bandwidth resources also goes to waste. Because even though communications among user terminals is closed and corresponding access lines of the user terminals becomes idle, bandwidth resources are still allocated fixedly to the idle access lines and not to reallocated to other busy access lines used by the other terminals.
In the method of statically bandwidths allocation for access lines in this way, it is difficult to use the bandwidths resources effectively according to communications states of the respective access lines.
As a related technical document, a technique concerning the xDSL entitled “Data Transmission Network” is disclosed in Japanese Patent Application Laid-Open No. 2004-519974 corresponding to the International Publication No. WO 02/089459 A1 of the PCT. This technology relates to a data transmission network for data transmission which allows xDSL data transmission and voice data transmission between a backbone network and a network termination device on any data transmission medium such as a copper telephone line. However, the document does not disclose a technique related to bandwidth control.